A Universal Criterion for Plastic Yielding of Metallic Glasses with a(T/Tg)2/3Temperature Dependence
Room temperature (${T}_{R}$) elastic constants and compressive yield strengths of $\ensuremath{\sim}30$ metallic glasses reveal an average shear limit ${\ensuremath{\gamma}}_{C}=0.0267\ifmmode\pm\else\textpm\fi{}0.0020$, where ${\ensuremath{\tau}}_{Y}={\ensuremath{\gamma}}_{C}G$ is the maximum resolved shear stress at yielding, and $G$ the shear modulus. The ${\ensuremath{\gamma}}_{C}$ values for individual glasses are correlated with $t={T}_{R}/{T}_{g}$, and ${\ensuremath{\gamma}}_{C}$ for a single glass follows the same correlation (vs $t=T/{T}_{g}$). A cooperative shear model, inspired by Frenkel's analysis of the shear strength of solids, is proposed. Using a scaling analysis leads to a universal law ${\ensuremath{\tau}}_{CT}/G={\ensuremath{\gamma}}_{C0}\ensuremath{-}{\ensuremath{\gamma}}_{C1}(t{)}^{2/3}$ for the flow stress at finite $T$ where ${\ensuremath{\gamma}}_{C0}=(0.036\ifmmode\pm\else\textpm\fi{}0.002)$ and ${\ensuremath{\gamma}}_{C1}=(0.016\ifmmode\pm\else\textpm\fi{}0.002)$.